1. Field of the Invention
This invention relates to an electromechanical torque limiter for actuators and zone valves in heating, cooling and ventilation systems.
2. Description of Related Art
Heating and cooling systems typically employ hydronic valves or damper valves (or other devices to be actuated) with actuators to control the flow of fluid such as water, air, or gas to specific zones of a heating and air conditioning system and are usually referred to as zone valves. Typically, the zone valves are actuated to affect environmental conditions in specific zones in response to thermostats distributed throughout the heating and air conditioning system.
Conventional zone valves are actuated by an electric motor that opens or closes the valve in one direction while a spring mechanism assists in closing or opening the valve in the opposite direction. These motorized conventional valves rotate the valve element to its closed position by rotating a motor shaft through a gear mechanism. The shaft rotates a ball valve element, or a vane element, to its open or closed positions in the case of hydronic valves or damper valves, respectively. The valve is maintained in a closed position by continuously energizing the motor and applying a closing force to the valve element through the torque developed in the motor shaft.
In conventional zone valves, as the valve element moves from an open/closed position to a closed/open position, a return assist spring is tensioned so that the energy stored in the spring assists the valve element return to its previous position. Because these valves rely on the torque developed in the motor shaft to maintain the valve element in a closed/open position if the motor is simply de-energized the tensioned spring will return the valve element to its previous state, thus opening/closing the valve. It can be seen that in heating and air conditioning systems utilizing conventional motorized zone valves, the motor must be continuously energized in order to keep the valve port closed/open.
Motorized zone valves may have two or more ports. Zone valves incorporating multiple ports generally do not apply evenly distributed forces to the valve element. In one direction a motor is used to apply a closing force to the valve element and to tension a return assist spring. The shaft rotates the valve element from an open to a closed position against a first valve seat, the motor being continuously energized to maintain the valve port closed. When the motor is de-energized, the valve element utilizes the energy stored in the tensioned spring to apply a closing force against a second valve seat at a second port.
Conventional motorized zone valves relying on continuously energized motors to apply a closing force to a valve element against a first valve seat and relying on spring forces for applying a closing force to the valve element against a second valve seat suffer several disadvantages.
First, energy is wasted and the life expectancy of a motor is greatly reduced because the motor is generally stalled in its operation in order to maintain a continuous closing force against the valve seat.
Second, closing forces translated to a valve seat will fluctuate as the electrical power fluctuates in the electrical system, causing fluctuations in the amount of torque developed at the motor shaft. Manufacturing tolerances and component wear also affect the maintenance of closing forces without fluctuations.
Third, it is difficult to achieve symmetrical valve element closing forces acting against a first and a second valve seat because of the different mechanisms used to apply the closing forces, e.g. torque developed by the motor on one valve seat and spring force on the other valve seat.
Fourth, a motor in a conventional zone valve cannot be de-energized because it must apply a continuous closing force against the valve element to overcome the force stored in the spring and the upstream port pressure in the heating, cooling and ventilation system. Thus, if the motor is de-energized, the valve element will tend towards opening the valve port instead of maintaining a tight seal. In addition, the valve element cannot be maintained in a partial stroke position to modulate flow in mixing applications.
Fifth, conventional zone valve actuators cannot compensate for dimensional tolerance variations caused by heat expansion, contraction, and seating of elastomeric materials.
Therefore, it can be seen that there is a need for a zone valve apparatus having an electromechanical torque limiter that provides energy savings by allowing a motor to be de-energized after a predetermined valve element closing force is achieved and maintaining a constant closing force against the ball valve element without requiring the motor to be energized.
It can also be seen that there is a need for an electromechanical torque limiter for a zone valve actuator that is not affected by voltage variations, component wear or manufacturing tolerances.
It can also be seen that there is a need for a zone valve apparatus having an electromechanical torque limiter which allows the application of symmetrical closing forces to a valve element acting against a first valve seat and subsequently acting on a second valve seat. It can also be seen that there is a need for a zone valve apparatus having an electromechanical torque limiter that provides a self locking gear mechanism to hold the valve element in a partial stroke position within the valve housing for providing flow modulation in mixing applications without the need for additional components.
It can also be seen that there is a need for a zone valve apparatus having an electromechanical torque limiter to compensate for dimensional variations caused by heat expansion, contraction, and compression setting of elastomeric materials.